If you ever need a voltage level lower than the voltage source you have.
One of the easiest and cheapest ways to do it is by using a voltage divider.
This is basically by putting two resistors in series
and then tapping into the node between them.
And so, by choosing the value of those resistors,
you can get exactly the voltage you want,
if you know the incoming voltage on that spot right there in the middle.
So, we are gonna go over that a little bit. I'm gonna talk about some of the pros and cons
and we're going to do a quick demonstration.
So, with that, I set up a very simple voltage divider, right here. And let's do some measurements.
And show what we're expecting to get versus what we actually get
and the similarities plus some of the drawbacks.
So, I have it right now to measure the resistance. So what we're gonna call R1 is, it's about 100 kiloohms.
So, I'm gonna go into here, I'm gonna put 5 volts because I know that's what I'm gonna set it to.
And R1 is going to be 100 kiloohms. And then, R2 is 149.7 basically a 150 kiloohms.
So, with that we should be seeing 2 volts over R1 and 3 volts over R2 as soon as we hooked this up.
So, I'm gonna hook it up and turn on the power, and it's showing 5 volts.
So now, I'm going to measure my voltage.
So, R1 is measuring 2.02 volts and R2 is measuring 3.025 volts which makes perfect sense.
And even the slight variations from exactly 2 volts and 3 volts is because these are only 5 percent tolerance resistors.
And as we measured this one wasn't 150 kiloohms, it's a 149 point something kiloohms,
and this one wasn't exactly a hundred so that's the only reason the variation.
Again beautiful thing about resistors and voltage and current
is that they are very linear and they work together perfectly.
So, this seems great! So why don't we use this method to get the voltage we want all the time.
And with that I'm gonna put a load in there.
So, let's measure this load refresh my memory.
So, this resistor is measuring at 1.46 kiloohms. It's probably 1.5 or 1500 ohm resistor.
So, let's put this in parallel with R2. So, assuming we want to have three volts across this.
Let's put this in here, I have it share the same ground, okay.
So, now it's in there nice and pretty, let me turn the output back on,
switch us back to voltage and let's measure this load resistor
because it's supposed to have three volts across it.
So, as I measure across it, we will see I'm backwards but still it's showing about 72 millivolts
and that's obviously much much less than the three volts that we are expecting
and this is pretty obvious if you think about it for just a brief moment.
And that is now, the 150 kiloohm resistor is in parallel with the 1.5 kiloohm resistor.
So, that's gonna give our equivalent resistance of less than 1.5 kilohms probably around 1.4-ish eight or something like that.
So, we can go back to the calculator and assume that that's 1.48
And now it's showing that our voltage output is, yeah about 72, 73 millivolts
which is actually surprisingly close to what we got here.
And that is the biggest issue with the voltage divider, is if you have a low impedance load
that's trying to use that voltage it's just not going to work .
Now, if you have an extremely high impedance load, if that was a 1 megaohm resistor,
it would still affect it because it has a resistance. But, it's so big that it would be a very minimal effect.
So, that is again, the biggest problem with the voltage divider is,
it just can't handle even this relatively low impedance loads.
Now, another problem is as we even went over it,
the measured resistance was or the measured voltage was not exactly what we were expecting
and that's because these are 5 percent tolerance resistors.
And if you need an exact, exact voltage then you need to have the higher tolerance
and therefore the more expensive resistors.
So, those are two of the big drawbacks with these.
Now, to overcome the drawback of the drooping, why don't we just make these two resistors smaller.
So, instead of a 100 kiloohms and a 150 kiloohms, why don't we make them 1 kiloohm and 1.5 kilohms.
And that way, having another 1.5 kilo ohm resistor in there, instead of dropping it to 72 millivolts
that will still drop it significantly but at least it'll be reasonable.
And the problem with that is with 150 kiloohms and 100 kiloohms in series, you're getting 250 kiloohms.
So 5 volts over 250 kiloohms and that puts you in I think about the 20 microamp current.
So, you take both of those and you drop them down by two orders of magnitude
and your current then goes up by two orders of magnitude.
So, instead of 20 microamps, you're gonna be getting more like 2 milliamps
And so, your power dissipation is gonna be going up by orders of magnitude.
And that's one of the trade-offs of decreasing the value of those resistors
and making them a little bit more robust of a voltage divider.
So, it's a lot of trade-off, it's a lot of difficulty.
But, there are a couple of things we can use this for. Again, if you're doing like in ADC,
you just need a reference voltage for an analog to digital converter.
This is perfect because ADCs just need a reference voltage, they're gonna be extremely high impedance.
And you just want to say "Hey, I need my ADC to go from 0 to 3 volts instead of 0 to 5 volts".
You do something like this and it's gonna have minimal load and it should work great.
But if you ever are needing to actually power something, something that's going to consume even a measurable amount of power.
Yeah, this isn't really the method you want to follow.
Now, another interesting thing is that voltage dividers actually come in a prepackaged form
and that is a potentiometer.
So, potentiometers, the way these work is you basically have an input/output and a middle one.
So, if I were to have the same setup here, I'd put 0 volts here, 5 volts here.
And then that middle one is going to change voltage depending on how I rotate this.
So, instead of doing something like this, this is a variable voltage divider.
And it's very common to use these in microcontrollers.
Actually, the most common thing for hobbyists is to use these and hook it up to an ADC.
And then have it pinging this every once in a while
to check to see what value of, most often like how bright you want your LEDs
So, if it's all the way, one way, you'll do a 100 percent duty cycle on your LED then 15, 25, 0 percent.
And so, this is extremely common but that's all that's happening in here is,
this is basically just a variable voltage divider packaged up in a nice convenient package.
So, same thing this this kind of looks like that, mine is that one of course and that's it.
I mean voltage dividers, they're very simple, they're easy to use.
You can use one of our tools on CircuitBread.com
to either figure out exactly voltage you're gonna get depending on the resistors you get or we also have a way to make it
So, it can choose the resistors you need to use depending on the power dissipation you're willing to use.
And also the incoming voltage.
So, while voltage dividers aren't great for powering things,
and you really want to look at either a linear switching power supply for something like that
or an LDO something that is designed specifically for powering things at a different voltage.
These are great one just it's really good to understand
to get an intuitive feel of how the resistors in series, working in parallel and just get a good understanding
because that's gonna help you in any electronics or engineering things you work on.
And then, also again it's can be very helpful and very cheap,
very inexpensive, cheap and inexpensive are obviously the same thing.
But very inexpensive and very easy things to do if you are trying to get something
that just needs a high impedance source for the voltage.
Alright! That's it for now, please make sure to go check out our site CircuitBread.com
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